1. Field of the Invention:
The present invention relates to a speed stabilization apparatus for use in a two shaft gas turbine, and more particularly to a speed stabilization apparatus for use in a two shaft gas turbine which can improve load charging dip characteristics; that is a momentarily reduction of a rotational speed of a generator when a charging load is additionally connected to an output of the generator.
2. Description of Prior Art:
A well-known two shaft gas turbine employs a compressor driving shaft connected to a compressor driving turbine for driving a compressor, and a load driving shaft connected to an output turbine for driving a generator which is a load of the turbine, wherein these shafts are driven independently. Such a two shaft gas turbine usually incorporates a governer as a speed stabilization means. The governor is so designed that it responds to a rotational speed signal representing a rotational speed of the load driving shaft, and opens a fuel valve by a suitable degree when the rotational speed of the load driving shaft is lowered, so as to increase the amount of combustion gas supplied to the turbine from a combustor thereby causing an increase in the speed of the turbine, while when the rotational speed of the load driving shaft is increased it closes the fuel valve by a suitable degree so as to reduce the amount of combustion gas, thereby causing a decrease in the speed of the turbine. In this manner, the governer can stabilize the variation of the rotational speed of the generator resulting from a change in the electrical load to be connected to an output of the generator, and hence the output frequency of the generator can be stabilized.
According to the generator driven by the two shaft turbine provided with a speed stabilization apparatus comprised of the conventional governor mentioned above, since the compressor driving shaft is in principle independent of the load driving shaft, if a basic load normally charged to the generator is light, the compressor driven by the compressor driving shaft is caused to rotate at a speed much below that of the output turbine for the generator driven by the load driving shaft the speed of which is directly regulated by the governer so that the rotational speed of the generator is maintained at a level equal to that of the generator charged a rated load, whereby a highly efficient operation may be ensured at the time of light loading.
Conversely, when a large amount of load is additionally charged to the light basic load, the governer is activated to regulate the speed in response to the reduction of the rotational speed of the load driving shaft. In this case, since the compressor is rotated at a low speed and little air is supplied from the compressor to the combustor, even if the fuel valve is opened quickly, the combustion gas will not be actively supplied from the combustor so quickly. Thus, the rotational speed of the load driving shaft cannot be immediately returned to the previous higher speed and as a consequence a load charging dip may be caused in the rotational speed at the time of high load charging.
It is conceivable, in order to solve this load charging dip problem, to employ a single shaft gas turbine adapted to drive a compressor and a generator with one shaft. According to the monoaxial gas turbine, since the compressor is driven by the same driving shaft the rotational speed of which is governed to be at a constant and fixed speed even against a light basic load, and thus the compressor will not rotate at a reduced rotational speed at the time of light loading, an immediate response of the compressor may be secured and no or little load charging dip will be experienced. On the contrary, however, a high efficiency under a light basic load or partial load charging, cannot be anticipated. In view of the contradictory problems in terms of immediate response and high efficiency with regard to the two shaft gas turbine and the monoaxial gas turbine, there has been a demand for a speed stabilization apparatus for a two shaft gas turbine which is capable of simultaneously solving both the above problems.